The requirements for protection of a motor drive against electric shock are presented e.g. in the standards IEC 61140: “Protection against electric shock. Common aspects for installation and equipment.”; IEC 60364-4-41: “Low-voltage electrical installations—Part 4-41: Protection for safety—Protection against electric shock”; IEC 60204-1: “Electrical equipment of machine”; IEC 61800-5-1: “Adjustable Speed electrical power drive systems—Part 5-1: Safety requirements—Electrical, thermal and energy”.
According to standard EN 61140 a fundamental rule of protection against electric shock is that hazardous-live parts shall not be accessible and that accessible conductive parts shall not be hazardous live in normal circumstances or as a consequence of a single fault. For these reasons accessible conducting parts are normally earthed.